Polyphenylene sulfide (hereinafter abbreviated as PPS) is known as a high-melting heat resistant resin with excellent fluidity, organic solvent resistance, electrical characteristics, and flame retardance. For use as a molding material, however, PPS has poor extrusion stability and has poor molding stability due to the low degree of polymerization reached. Further, the glass transition temperature of PPS is not very high and as a result PPS undergoes a considerable reduction in rigidity at high temperatures. Improvements in performance have been achieved by compounding PPS with inorganic fillers such as glass fiber, carbon fiber, talc, and silica. However, molded articles obtained from PPS compositions containing these types of inorganic fillers tend to suffer from deterioration of appearance or warpage.
On the other hand, polyphenylene ether (hereinafter abbreviated as PPE) is recognized as an engineering plastic with excellent heat resistance, dimensional stability, non-hygroscopicity, and electrical characteristics. However, PPE has poor moldability due to its low melt-flow characteristics and also has insufficient oil resistance and insufficient impact resistance.
Hence, various polymer blends containing PPS or PPE have hitherto been proposed in an attempt to provide a molding material in which the above-described drawbacks are compensated for while retaining their own advantages.
For example, blending PPE and PPS to improve moldability of PPE has been suggested as disclosed in JP-B-56-34032 (the term "JP-B" as used herein means an "examined published Japanese patent application"). However, a mere polymer blend, though exhibiting improved moldability, has poor affinity at the interface between the PPE and the PPS because these two resins are essentially incompatible with each other. As a result, the composition undergoes phase separation on molding, failing to provide molded articles having satisfactory mechanical strength.
In order to overcome the above-described problem of incompatibility between PPS and PPE, several proposals have been made to date. For instance, JP-A-59-164360 (U.S. Pat. No. 4,528,346) (the term "JP-A" as used herein means an "unexamined published Japanese patent application") suggests compounding an epoxy resin with a PPS/PPE blend, and JP-A-2-86652 (EP-A-360544) teaches compounding a PPS/PPE blend with an epoxy-containing styrene polymer. These proposed resin compositions achieve some improvement in compatibility between PPS and PPE but not to a sufficient degree, and the mechanical properties of the resulting molded articles are not regarded satisfactory.
It has also been proposed to modify PPE by introducing various functional groups to provide improved compatibility with PPS. For example, JP-A-64-36645 and JP-A-2-36261 (EP-A-341422) disclose compounds having an ethylenically unsaturated bond and an acid anhydride group in the same molecule, more specifically acid-modified PPE obtained by melt-kneading PPE with maleic anhydride. Further, JP-A-2-49023 (GB-A-2218996) discloses that the combined use of such acid-modified PPE and a polyisocyanate results in a further improvement in PPE/PPS compatibility. Furthermore, JP-A-1-259060 suggests that a combination of other modified PPE, specifically acid-modified PPE or hydroxyl-modified PPE obtained by melt-kneading PPE with hydroxyethyl acrylate, glycidyl methacrylate, etc., and functionalized modified PPS provides a resin composition having excellent mechanical strength. None of these proposals, nevertheless, is deemed to result in sufficient compatibility between PPE and PPS. A melted acid-modified PPE itself is not sufficiently compatible with PPS. Moreover, the techniques are accompanied by undesired problems. That is, modification by kneading in an extruder results in instability when drawing strands of the compound; or by-products which are unfavorable for performance of the final composition, such as an unreacted modifier and dissolved or insoluble gel of volatile low-molecular compounds including thermal decomposition products, must be removed. Therefore, development of a process for producing modified PPE having improved compatibility with PPS, while settling these problems, would make it possible to provide an excellent resin composition which meets the demands for high performance.